Prospective Evaluation of an Intraoperative Synovial Calprotectin Point-of-Care Lateral Flow Test for Periprosthetic Joint Infection in Hip and Knee Revisions.

BACKGROUND: Synovial calprotectin measured by lateral flow assay (LFT) has emerged as a promising point-of-care (POC) biomarker for periprosthetic joint infection (PJI). However, existing studies are limited by retrospective designs, frozen sample use, off-label stool test application, and small sample sizes. This prospective study evaluated the diagnostic accuracy of an intraoperative synovial calprotectin POC-LFT in hip and knee revision arthroplasty.

METHODS: A consecutive cohort of 80 patients undergoing revision total hip or knee arthroplasty (THA, TKA) was prospectively enrolled between March 2022 and February 2026. The 2018 International Consensus Meeting (ICM) criteria served as the reference standard. Among 55 THA revisions, 24 patients had PJI and 31 had aseptic failure. Among 25 TKA revisions, eight had PJI and 17 aseptic failure. Synovial fluid was aspirated intraoperatively and tested fresh using a dedicated calprotectin LFT. Using a threshold of ≥ 50 mg/L, sensitivity, specificity, predictive values, and area under the receiver operating characteristic curve (AUC) were calculated.

RESULTS: Median calprotectin was 138 mg/L in infected versus seven mg/L in aseptic THA patients. Sensitivity was 91.7% (95% confidence interval (CI), 73.0 to 99.0), specificity 90.3% (95% CI, 74.2 to 98.0), and AUC 0.894 (95% CI, 0.81 to 0.98). Median calprotectin was 106.5 mg/L in infected versus seven mg/L in aseptic TKA patients. Sensitivity was 87.5% (95% CI, 47.3 to 99.7), specificity 100% (95% CI, 80.5 to 100), and AUC 0.930 (95% CI, 0.84 to 1.00). There were three false-positive cases (metallosis, recent dislocation, and unexplained inflammation), while three false-negatives were associated with fungal pathogen and culture-negative PJI with sinus tract.

CONCLUSION: The intraoperative synovial calprotectin POC-LFT demonstrated high diagnostic performance in both THA and TKA revisions using a threshold of 50 mg/L. Its rapid turnaround time and high negative predictive value make it a reliable adjunct for real-time surgical decision-making within a comprehensive diagnostic framework.